Dry conditions are likely to continue across the Far West region following last year’s drought, which helped the current megadrought secure the title as the driest in at least 1,200 years, according to a new study.
The study, “Rapid intensification of the emerging southwestern North American megadrought in 2020-2021,” was published Feb. 14 in the journal Nature Climate Change. According to its findings, the current 22-year-old drought in southwestern North America is the driest megadrought since at least the year 800. A megadrought is a drought that lasts two decades or longer.
The study points to human-caused climate change as being responsible for 42 percent of the megadrought.
“Climate change is changing the baseline conditions toward a drier, gradually drier state in the West, and that means the worst-case scenario keeps getting worse,” study lead author Park Williams, a climate hydrologist at University of California, Los Angeles, told the Associated Press.
“This is right in line with what people were thinking of in the 1900s as a worst-case scenario. But today I think we need to be even preparing for conditions in the future that are far worse than this.”
In the study, researchers calculated the intensity of droughts by analyzing tree rings, which give insight about soil moisture levels each year. Their measurements were then checked against historical climate data, which showed periods of severe drought marked by high degrees of soil moisture deficit.
The researchers studied the Pacific Ocean to the Rocky Mountains and southern Montana to northern Mexico. They determined megadroughts occurred repeatedly in the region from 800 to 1600, and Williams noted the finding shows dramatic shifts in water availability happened in the Southwest well before the effects of human-caused climate change became apparent in the 20th century.
“Without climate change, the past 22 years would have probably still been the driest period in 300 years,” Williams said. “But it wouldn’t be holding a candle to the megadroughts of the 1500s, 1200s or 1100s.”
Current drought
As of Feb. 10, drought across the West was widespread, according to the Drought Monitor. At least 95 percent of the region is in some stage of abnormally dry conditions, and 64 percent of the region is in some severity of drought. About 20 percent of the region is in extreme drought, and close to 4 percent is in exceptional drought.
Through the week ending Feb. 12, western Oregon saw expansions of moderate and severe drought, although the northern Oregon Cascades saw improvement. Extreme drought expanded through Utah. The rest of the West was relatively unchanged, although weeks of dry weather have caused high elevation snowpack levels in the West to decline from the above-normal levels seen in the beginning of the year, according to the Drought Monitor.
Snowpack
The West experienced an above-normal snow water equivalent at the beginning of 2022, which provided a buffer to mitigate the extremely dry conditions over the past month, according to the National Integrated Drought Information System’s (NIDIS) latest snow drought report. This buffer helped most of the region avoid plummeting into a snow drought.
However, the West is trending toward snow drought conditions. The region’s snow water equivalent is below normal at 62 percent of snowpack telemetry (SNOTEL) sites as of Feb. 8, compared to 21 percent just one month earlier, according to NIDIS.
Snow drought occurs when there is a period of abnormally low snowpack, and it can reduce both summer and winter water availability. This can lead to severe impacts, affecting ecosystems, reservoir levels and water resource management, among others.
NIDIS reported zero precipitation over the past 30 days (as of Feb. 10) at many SNOTEL sites in northwest California, the Sierra Nevada and the Great Basin. However, “Remarkably, some of the sites at which zero snow fell in the past month still have slightly above-normal snow water equivalent thanks to major storms during the last two weeks of December and beginning of January,” the report read.
Peak snow water equivalent is used to assess the potential water supply outcome, which generally occurs from late March through early April. With more than a month left in the heart of the snow season, many areas have already exceeded 70 percent of median peak snow water equivalent, NIDIS said, thanks to the wet period in early winter.
In the Cascades of Oregon, several SNOTEL sites have already exceeded the median peak snow water equivalent. However, there are numerous areas that have received less than 50 percent of the median peak snow water equivalent, such as northwest California, northeast Nevada, Utah, northwest Wyoming and southwest Montana. Below-average precipitation and snowfall is likely to continue during the next couple weeks in most of the West.
“The continued dry spell, above-normal temperatures, and increasing late winter sun angles all will be working against snowpack accumulation, and the spatial extent of snow drought is likely to continue to increase,” the report read. — Anna Miller, WLJ managing editor
